I just had a really good question come through my e-mail, and I figured this is the perfect place to share it.
Q- I have a couple of hundred Copic markers now and plan to take them with me while traveling which means they will be left in a hot car for several hours one day. Will this hurt them in any way? If it will I could take a cooler.
A- No this won't hurt your markers, they are very air tight
Let me tell you a little story...
Our European counterpart had a shipment of markers get stuck in the Saudi Desert during the Persian Gulf War. They were stuck in the desert for about 5 months, in temps of over 120º F. When they got the markers back they were sure that all had been ruined, however NONE of them had any problems. All were juicy and good.
I have left them in a hot car on many occasions with no problems, as they are super air tight. The only problem you may have is if you color with them in super-hot weather and then you next color with them in a much cooler temp or much higher elevation. The marker will have picked up the air pressure of the first climate and may blob upon use in the other air pressure. Just pull the caps off both sides and then their air pressure will return to normal and you won't have any problems. (this happened to me last summer).
For more marker travel tips you can check this post I made last summer. Happy Traveling!